Electromagnetic Wave Attenuation Film

Abstract

To provide an electromagnetic wave attenuation film that can attenuate radio waves in the millimeter wave band and is a thin electromagnetic wave attenuation film that has excellent environmental resistance such as weather resistance and heat resistance. The present invention provides an electromagnetic wave attenuation film comprising a dielectric substrate having a front surface and a back surface, a thin-film conductive layer disposed on the front surface, and a flat inductor or laminating layer disposed on the back surface, and a topcoat layer made of a resin material may be provided on the thin-film conductive layer. The thin-film conductive layer is an electromagnetic wave attenuation film that includes a plurality of metal plates and satisfies the following formula in the frequency band of 57 GHz to 90 GHz, where T is the thickness of the metal plates and d is the skin depth: -2.5 ≦ ln(T / d) ≦ -1.0

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION Embodiments of the present invention relate to an electromagnetic wave attenuation film capable of capturing incident waves and attenuating reflected waves. [Background technology]

[0002] Radio waves with a frequency band of several gigahertz (GHz) are used in mobile communications such as mobile phones, wireless LAN, and electronic toll collection systems (ETC).

[0003] As an electromagnetic wave absorbing sheet for absorbing such electromagnetic waves, Patent Document 1 proposes a laminated sheet in which a rubber-like electromagnetic wave absorbing sheet and a paper-like sheet material such as cardboard are laminated together. Furthermore, with the aim of absorbing radio waves in higher frequency bands, Patent Document 2 proposes a radio wave absorbing sheet that can absorb radio waves in frequency bands of 20 GHz or higher by aligning the longitudinal direction of flat soft magnetic particles with the surface direction of the sheet.

[0004] It is also known that a radio wave absorber having a packed structure of particles with epsilon iron oxide (ε-Fe2O3) crystals in the magnetic phase exhibits radio wave absorbing performance in the range of 25 to 100 GHz (see Patent Document 3).

[0005] Patent Document 4 proposes a metal thin film-plastic composite film with linear scratches suitable for an electromagnetic wave absorber, which has a plastic film and a single-layer or multi-layer metal thin film provided on at least one surface of the plastic film, and in which a large number of substantially parallel, intermittent linear scratches are formed in multiple directions with irregular widths and intervals on the metal thin film. Patent document 5 discloses a radio wave absorbing structure that includes a resonant layer in which multiple patch conductors having individual resonant frequencies are arranged in a predetermined periodic pattern, a dielectric layer that multiple-reflects radio waves resonated in the resonant layer, and a reflective conductor layer that reflects radio waves incident from the dielectric layer toward the dielectric layer.

[0006] The electromagnetic wave absorbing sheets described above are used in electronic devices as well as for the interior decoration of buildings, etc. As described in Patent Document 6, acrylate copolymer-modified resins such as epoxy resin, polyurethane resin, chlorinated rubber resin, vinyl chloride resin, alkyd resin, unsaturated polyester resin, and epoxy acrylate resin are used as the electromagnetic wave absorbing material. Rubber-based materials such as polyamideimide and synthetic rubber are also used, as described in Patent Document 7. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-233834 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-198163 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-060484 [Patent Document 4] International Publication No. 2010 / 093027 [Patent Document 5] Japanese Patent Publication No. 2020-009829 [Patent Document 6] Patent No. 2612592 [Patent Document 7] Japanese Patent Application Laid-Open No. 2006-86422 Summary of the Invention [Problem to be solved by the invention]

[0008] In recent years, the practical application of wireless communication using millimeter wave bands above 30 GHz has progressed in order to enable larger volumes of data to be transmitted and received, faster communication speeds, and simultaneous multi-point connections, and the development of millimeter wave compatible devices that make this possible is progressing.In addition, the use of automotive radar equipment that utilizes extremely narrow directivity is also progressing.

[0009] Interference caused by diffuse reflection of electromagnetic waves within a device's housing can cause the device to malfunction. Therefore, suppressing electromagnetic noise is an important aspect of electromagnetic wave utilization technology. One method of suppressing electromagnetic noise is to use electromagnetic wave absorbing sheets such as those mentioned above, but at present, most of them are compatible with frequencies from 20 GHz to several tens of GHz, and are not compatible with the millimeter wave band. Although electromagnetic wave absorbing sheets that absorb electromagnetic waves in the millimeter wave band exist, they are not currently in practical use. The sheets used are thick to maintain absorption performance. It is difficult to suppress electromagnetic noise by incorporating it into the chair housing.

[0010] In view of the above, an object of the present invention is to provide a thin electromagnetic wave attenuation film capable of attenuating electromagnetic waves in the millimeter-wave band. Furthermore, because electromagnetic wave absorbers installed in electronic devices, building interiors, and the like are used continuously for long periods of time, another object of the present invention is to provide an electromagnetic wave attenuation film with excellent environmental resistance, such as weather resistance and heat resistance. The electromagnetic wave attenuation film of the present invention is considered to be a film capable of steadily localizing an electromagnetic field. In other words, the electromagnetic wave attenuation film of the present invention is considered to be a film capable of capturing an electromagnetic field. "Capturing" an electromagnetic field refers to the ability to achieve a state in which an electric field and a magnetic field are steadily localized. Furthermore, the captured electromagnetic field is partially absorbed by being converted into heat, and partially re-emitted. In other words, the energy of the captured electromagnetic field is converted into heat energy and the energy of the re-emitted electromagnetic wave. Since this re-emission is generally considered to have low directionality, it is considered that electromagnetic waves in the direction of specular reflection are reduced, and the reflected wave is attenuated. Therefore, reflected electromagnetic waves can be attenuated by absorption due to conversion of incident electromagnetic waves to heat and scattering due to re-emission. Because electromagnetic waves are attenuated by such a mechanism different from conventional ones, it is possible to attenuate them with a thin structure that is one-fourth or less of the wavelength, which was previously thought to be impossible. Furthermore, according to the embodiment of the present application, it is incredibly possible to attenuate them with a structure that is one-tenth of the wavelength. -2 It is possible to obtain a film capable of attenuating electromagnetic waves with custom thickness. [Means for solving the problem]

[0011] The present invention provides an electromagnetic wave attenuation film comprising a dielectric substrate having a front surface and a back surface, a thin-film conductive layer disposed on the front surface, and a flat inductor or a laminating layer disposed on the back surface, and a top coat layer made of a resin material may be provided on the thin-film conductive layer. The thin-film conductive layer is an electromagnetic wave attenuation film that includes a plurality of metal plates and satisfies the following formula in the frequency band of 57 GHz to 90 GHz, where T is the thickness of the metal plates and d is the skin depth: -2.5 ≦ ln(T / d) ≦ -1.0

[0012] Another electromagnetic wave attenuation film according to the present invention is used in the 57 GHz to 90 GHz frequency band and comprises a dielectric substrate having a front and a back surface, a thin-film conductive layer disposed on the front surface, and a flat inductor or laminating layer disposed on the back surface. The dielectric substrate has an uneven surface on the front surface, consisting of a first region that is a relatively low concave portion and a second region that is relatively high. The thin-film conductive layer includes a plurality of metal plates disposed in the first region. The first regions are disposed discretely, and the second regions are disposed between the plurality of first regions. A topcoat layer made of a resin material may be formed on the thin-film conductive layer. [Effects of the Invention]

[0013] According to an embodiment of the present invention, it is possible to provide a thin electromagnetic wave attenuation film that can attenuate radio waves in the millimeter wave band and that has excellent weather resistance. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic plan view showing an electromagnetic wave attenuation film according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing a part of a cross section taken along line II in FIG. [Figure 3]FIG. 2 is a schematic diagram showing a part of the cross section taken along line II in FIG. 1 when a top coat layer is provided. [Figure 4] 10A and 10B are images showing the simulation results of the electric field strength when there is no support cage, and (b) is a partially enlarged view of (a). [Figure 5] 10A and 10B are images showing the simulation results of the electric field strength when a support cage is provided, and FIG. 10B is a partially enlarged view of FIG. [Figure 6] FIG. 3 is a schematic plan view showing an electromagnetic wave attenuation film according to a second embodiment of the present invention. [Figure 7] FIG. 7 is a schematic diagram showing a part of a cross section taken along line II-II in FIG. [Figure 8] FIG. 7 is a schematic diagram showing a part of the cross section taken along line II-II in FIG. 6 when a top coat layer is provided. [Figure 9] 10 is a graph showing a simulation result of the attenuation of electromagnetic waves depending on the thickness of the metal plate. [Figure 10] 10 is a graph showing the electromagnetic wave attenuation characteristics at 57 GHz of Example 1A. [Figure 11] 10 is a graph showing the electromagnetic wave attenuation characteristics at 66 GHz of Example 1A. [Figure 12] 10 is a graph showing the electromagnetic wave attenuation characteristics at 71 GHz of Example 1A. [Figure 13] 10 is a graph showing the electromagnetic wave attenuation characteristics at 81 GHz of Example 1A. [Figure 14] 10 is a graph showing the electromagnetic wave attenuation characteristics at 86 GHz of Example 1A. [Figure 15] 10 is a graph showing the electromagnetic wave attenuation characteristics at 90 GHz of Example 1A. [Figure 16] 10 is a graph showing electromagnetic wave attenuation characteristics according to the proportion of metal area at 81 GHz in Example 1B. [Figure 17] 10 is a graph showing the electromagnetic wave attenuation characteristics when the metal plate is rectangular in shape in Example 1C. [Figure 18] 10 is a graph showing the electromagnetic wave attenuation characteristics when the metal plate has a hexagonal shape in Example 1C. [Figure 19] 10 is a graph showing the electromagnetic wave attenuation characteristics when the metal plate has a convex shape in Example 1C. [Figure 20] 10 is a graph showing the electromagnetic wave attenuation characteristics when the metal plate has a triangular shape in Example 1C. [Figure 21] 10 is a graph showing the electromagnetic wave attenuation characteristics when the metal plate is cross-shaped in Example 1C. [Figure 22] 10 is a graph showing the electromagnetic wave attenuation characteristics in Example 1A. [Figure 23] 10 is a graph showing electromagnetic wave attenuation characteristics in Example 2. [Figure 24] 10 is a graph showing the electromagnetic wave attenuation characteristics when a top coat layer is provided in Example 1A. [Figure 25] 10 is a graph showing the relationship between the dimensions of a metal plate and the wavelength of an electromagnetic wave that is attenuated. DETAILED DESCRIPTION OF THE INVENTION

[0015] The electromagnetic wave attenuation film 1 comprises a dielectric substrate (dielectric layer) 10, a thin-film conductive layer 30 formed on the front surface 10a of the dielectric substrate 10, and a planar inductor 50 formed on the back surface 10b of the dielectric substrate. The thin-film conductive layer is a thin layer of conductor. The thin-film conductive layer includes multiple metal plates. The thin-film conductive layer may also include a support cage (described later). The planar inductor is conductive, and an external magnetic flux generates a current inside the planar inductor near its surface. The current also generates a magnetic field outside the planar inductor near its surface. The planar inductor can be shaped like a slab. The dielectric substrate is an insulating substrate sandwiched between the thin-film conductive layer and the planar inductor. In other words, the thin-film conductive layer and the planar inductor are spaced apart in the thickness direction of the dielectric substrate, sandwiching the dielectric substrate between them. The front surface can be the surface on which electromagnetic waves are incident. The back surface is the surface of the dielectric substrate opposite the front surface. The dielectric substrate 10 may have a first region 121 with a relatively low front surface and a second region 122 with a relatively high front surface surrounding the first region. The thin-film conductive layer located on the second region 122 is referred to as a support cage. In other words, the thin-film conductive layer includes a support cage on the second region 122. Furthermore, when the electromagnetic waves attenuated by the electromagnetic wave attenuation film have a frequency f at which they reach a single minimum value, this frequency f is defined as the central attenuation frequency f. When the electromagnetic waves attenuated by the electromagnetic wave attenuation film have multiple minimum values, the central attenuation frequency is defined as the average frequency of multiple frequencies that are -3 dB below the minimum value with the greatest attenuation. The central attenuation wavelength can be calculated by dividing the speed of light in the dielectric substrate by the central attenuation frequency f, which will be described later. The electromagnetic wave attenuation film 1 may also be provided with a top coat layer 200 for achieving impedance matching with air and for improving the weather resistance of the sheet.

[0016] Fig. 1 is a schematic plan view showing an electromagnetic wave attenuation film 1 according to a first embodiment of the present invention, Fig. 2 is a schematic view showing a part of a cross section taken along line II in Fig. 1.

[0017] The dielectric substrate 10 is made of a dielectric material and can form a capacitor by being sandwiched between conductive materials. The dielectric substrate 10 can be made of an insulating material. A typical example of a material constituting the dielectric substrate 10 is a synthetic resin. The type of synthetic resin is not particularly limited as long as it has sufficient strength, flexibility, and processability in addition to insulating properties. This synthetic resin can be a thermoplastic resin. Examples of synthetic resins include polyesters such as polyethylene terephthalate (PET); polyarylene sulfides such as polyphenylene sulfide; polyolefins such as polyethylene and polypropylene; polyamide, polyimide, polyamideimide, polyethersulfone, polyetheretherketone, polycarbonate, acrylic resin, and polystyrene. These materials may be used alone, or two or more types may be mixed or laminated. The dielectric substrate 10 may also contain conductive particles, insulating particles, magnetic particles, or a mixture thereof.

[0018] In an embodiment of the present invention, the thickness of the dielectric substrate can be sufficiently thin compared to the wavelength of the electromagnetic wave. It is known that when a dielectric substrate is sufficiently thin compared to the wavelength of the electromagnetic wave, no traveling waves are generated within the dielectric substrate. "Sufficiently thin" can be less than half the wavelength. Traveling waves are not guided when the thickness is less than half the wavelength. This is a phenomenon known as electromagnetic wave cutoff. Furthermore, the thickness can be less than one-tenth of the wavelength. Generally, when the difference in the propagation distance of an electromagnetic wave is less than one-tenth of the wavelength, no substantial phase difference occurs. In other words, when the distance between the metal plate and the planar inductor is less than one-tenth of the wavelength at the dielectric substrate, no substantial phase difference occurs between the electromagnetic wave re-emitted from the metal plate and the reflected wave from the planar inductor due to that distance. It is believed that electromagnetic waves do not guide within a sufficiently thin dielectric substrate sandwiched between conductors. Normally, electromagnetic waves are cut off (cutoff) when the substrate is so thin, and no electric or magnetic field is localized in such a dielectric substrate. Note that this wavelength in an embodiment of the present invention can be the attenuation center wavelength. Furthermore, unexpectedly, attenuation was achieved even when the dielectric substrate was less than 1 / 100 of the wavelength. This thickness is on the same level as the roughness of the most precise mirror surface, meaning that attenuation is achieved with a structure that is virtually thin compared to the scale of electromagnetic waves.

[0019] As a result of various experiments and simulations, the inventors have found that standing localization of electric and magnetic fields due to electromagnetic waves occurs even in a sufficiently thin dielectric substrate. The thickness of the dielectric substrate 10 can be 5 μm or more and 300 μm or less. Furthermore, the thickness of the dielectric substrate 10 can be 5 μm or more and 100 μm or less. This is thinner than half the wavelength of the millimeter wave band, and even thinner than one-tenth the wavelength of the millimeter wave band. Therefore, the electromagnetic wave attenuation film can attenuate electromagnetic waves in the millimeter wave band despite being a thin film. The thickness of the dielectric substrate 10 can be constant or variable.

[0020] The dielectric substrate 10 can be single-layer or multi-layer. The front surface of the dielectric substrate 10 may have an uneven surface. The dielectric substrate 10 may have a carrier 11 and an underlayer 12 on the carrier 11. The front surface of the underlayer 12 may have an uneven surface. The carrier 11 may be an extruded film. The extruded film may be a non-stretched film or a stretched film. The underlayer 12 may be composed of two layers: a molding layer and an anchor layer. Furthermore, an adhesive layer may be provided to improve adhesion between the underlayer 12 and the metal plate and the flat inductor. The underlayer 12, molding layer, anchor layer, and adhesive layer can be made of the same materials as those constituting the dielectric substrate.

[0021] The carrier 11 forms the back surface 10b of the dielectric substrate 10, and the underlayer 12 forms the front surface 10a of the dielectric substrate 10. If the front surface 10a has irregularities, it is preferable to provide an irregular structure on the underlayer 12. That is, the front surface 10a of the dielectric substrate 10 has irregularities corresponding to the irregularities of the underlayer 12, and the back surface 10b of the dielectric substrate 10 is generally flat. The characteristics of the electromagnetic wave attenuation film 1 change depending on the state of the unevenness of the front surface 10a, as will be described later.

[0022] The thin-film conductive layer 30 covers all or part of the front surface 10a in a plan view of the electromagnetic wave attenuation film 1. The flat inductor 50 covers all or part of the back surface 10b. As long as the performance of the electromagnetic wave attenuation film 1 is not significantly impaired, the flat inductor 50 may have a portion not covered by the thin-film conductive layer 30 or the flat inductor 50, for example, part of the periphery of the electromagnetic wave attenuation film 1.

[0023] The materials for the thin-film conductive layer 30 and the planar inductor 50 are not particularly limited as long as they are conductive. From the viewpoints of corrosion resistance and cost, aluminum, copper, silver, gold, platinum, tin, nickel, cobalt, chromium, molybdenum, iron, and alloys thereof are preferred. The thin-film conductive layer 30 and the planar inductor 50 can be formed, for example, by vacuum deposition on the dielectric substrate 10. The planar inductor 50 may also be made of a conductive compound. Furthermore, the planar inductor 50 may be a continuous surface or may have a pattern such as a mesh or patch. The thickness of the thin-film conductive layer 30 can be 10 nm or more and 1000 nm or less. If it is less than 10 nm, the function of attenuating electromagnetic waves may be reduced. If it exceeds 1000 nm, productivity may decrease. The planar inductor 50 can be a casting, a rolled metal plate, a metal foil, a vapor-deposited film, a sputtered film, or a plated film. The thickness of the rolled metal plate can be 0.1 mm or more and 5 mm or less. The thickness of the metal foil can be 5 μm or more and less than 100 μm. When the planar inductor 50 is a vapor-deposited film, a sputtered film, or a plated film, the thickness can be 0.5 μm or more and less than 5 mm. The thickness of the planar inductor 50 can be 0.5 μm to 5 mm. When the planar inductor 50 is a casting, the thickness is not specified, but the maximum dimension can be 10 mm or more. The thickness of the planar inductor 50 can be equal to or greater than the skin depth determined by the attenuation center wavelength. The thickness of the planar inductor 50 can be greater than the thickness of the thin-film conductive layer 30. The thin-film conductive layer 30 and the planar inductor 50 may be made of the same metal. This same metal may be the same pure metal or an alloy of the same metal (for example, both may be an aluminum alloy), or the thin-film conductive layer 30 may be made of a pure metal and the planar inductor 50 may be made of an alloy of the metal of the thin-film conductive layer 30. The thin-film conductive layer 30 and the planar inductor 50 may also be made of different metals. The thin-film conductive layer 30 may have a topcoat layer 200 on the surface opposite the dielectric substrate. FIG. 3 is a schematic diagram showing a portion of the cross section taken along line II in FIG. 1 when a topcoat layer is provided. The planar inductor 50 may also have a topcoat layer 200 on the surface opposite the dielectric substrate. The thickness of the topcoat layer 200 may be 0.1 μm or more and 50 μm or less, or even 1 μm or more and 5 μm or less. The topcoat layer 200 may be a single layer or multiple layers. The topcoat layer 200 may be made of a single material, a mixture, or a composite of urethane resin, acrylic resin, polyamide, polyimide, polyamideimide, epoxy resin, or silicone resin. It may also contain insulating particles, magnetic particles, conductive particles, or a mixture thereof. The particles may be inorganic particles. The topcoat layer 200 matches impedance with the air through which radio waves propagate, enabling radio waves to be effectively attenuated by the thin-film conductive layer. Furthermore, the thin-film conductive layer 30 and the planar inductor 50 can be endowed with corrosion resistance, chemical resistance, heat resistance, abrasion resistance, impact resistance, etc. For example, by using a cross-linked acrylic resin, a cross-linked epoxy resin, polyamide, polyimide, polyamideimide, silicone resin, etc., it is possible to improve solvent resistance and also heat resistance. Furthermore, by using a urethane resin, etc., it is possible to improve impact resistance, and by using a silicone resin, it is possible to improve abrasion resistance.

[0024] The dielectric substrate 10 may have a first region 121 with a relatively low front surface and a second region 122 with a relatively high front surface. The shape of the first region 121 in a plan view may be a square, hexagon, cross, other polygon, circle, or ellipse. The corners of the square, hexagon, cross, or other polygon may be rounded. The first regions 121 are arranged discretely. The first regions 121 are arranged in a two-dimensional matrix at a predetermined pitch. The second region 122 surrounds the first region 121 in a planar view of the electromagnetic wave attenuation film 1. The thin-film conductive layer 30 on the first region 121 includes a metal plate. That is, the metal plate is provided on the first region 121. In other words, the metal plate is located on the first region 121. The shape of the metal plate in a planar view can be a square, hexagon, cross, other polygon, circle, or ellipse. The corners of this square, hexagon, cross, or other polygon can be rounded. The second region 122 is formed in a mesh or lattice shape in a planar view according to the above-described aspect of the first region 121. The surfaces of the first region 121 and the second region 122 that come into contact with the thin-film conductive layer 30 are generally parallel to the back surface. Furthermore, they may have roughened surfaces partially or entirely. As will be described later, by roughening the surfaces of the first region 121 and the second region 122 that come into contact with the thin-film conductive layer 30 partially or entirely, the electrical resistance of the thin-film conductive layer 30 can be adjusted.

[0025] 2, the thin-film conductive layer 30 is formed on the upper surfaces of the first region 121 and the second region 122. On the other hand, the thin-film conductive layer 30 is not present on the side surface 122a of the second region 122 that extends above the first region 121, and the dielectric substrate 10 is exposed. This allows the thin-film conductive layer 30 in the first region 121 and the thin-film conductive layer 30 in the second region 122 to be electrically insulated from each other. As long as the electrically insulated state can be achieved, part of the side surface 122a may be covered with the thin-film conductive layer 30. The metal plate in each first region can have a shape that conforms to the shape of the first region 121 in a plan view. That is, the metal plate can have a shape that is the same as or similar to the shape of the first region 121 in a plan view. The dielectric substrate 10 may also include a plurality of metal plates that have the same shape and size in a plan view. Furthermore, the first regions 121 can be separated while remaining parallel to each other, and the arrangement density on the front surface can be generally uniform.

[0026] It is believed that the electromagnetic wave attenuation film 1, with the above-mentioned configuration, exhibits a unique mechanism at a specific wavelength.

[0027] An electromagnetic wave incident on the electromagnetic wave-attenuating film of the present invention behaves as follows: Specifically, the electromagnetic field and current generated by the incident wave are considered to be as follows:

[0028] First, according to Faraday's law, the fluctuation of the magnetic flux of the incident wave transmitted through the metal plate induces an AC current in the planar inductor 50 that is parallel to the plane of incidence of the planar inductor 50. According to Ampere's law, this AC current generates a fluctuating magnetic field in the dielectric substrate adjacent to the planar inductor 50. Furthermore, the fluctuating magnetic field becomes a fluctuating magnetic flux with the magnetic permeability as a coefficient.

[0029] The electric field generated by a fluctuating magnetic flux normally induces a current in a direction that suppresses the magnetic flux according to Henry's law. However, in the configuration of the present application, contrary to expectations, it acts in the opposite direction, enhancing the current. As a result, a current greater than that induced by the incident wave flows in the metal plate. In other words, although the area of ​​the metal plate is smaller than that of the planar inductor 50, it can generate a current similar to that of the planar inductor 50.

[0030] The direction of the current generated in this metal plate is opposite to that of the planar inductor 50. A closed circuit can be formed by the opposite currents flowing in the metal plate and the planar inductor 50, and the displacement current flowing between them. If the closed circuit is formed only between the metal plate and the planar inductor 50, and no electric flux is generated in the space outside the electromagnetic wave attenuation film that is parallel to the electromagnetic wave attenuation film, no reflected wave can be generated. Furthermore, the reflected wave by the planar inductor 50 and the electromagnetic wave re-emitted by the current in the metal plate are out of phase by π, so they cancel each other out.

[0031] According to the above principle, reflected waves are attenuated by the electromagnetic wave attenuation film. From the viewpoint of energy, it is believed that multiple mechanisms act synergistically as follows:

[0032] The first mechanism is the generation of a non-propagating, periodically oscillating electromagnetic field by the incident wave, as will be shown later by simulation of the magnetic field density. The planar inductor 50 induces magnetic flux in the tangential direction of the planar inductor 50 due to the incident wave. The induced magnetic flux generates an electric field extending from a pair of opposing sides of the thin-film conductive layer 30 (i.e., the metal plate) on the first region 121, perpendicular to the planar inductor 50. Next, when an electromagnetic wave is incident on the planar inductor, the fluctuating magnetic flux induces a current near the surface of the planar inductor. The current induced in the planar inductor generates a magnetic field in the dielectric substrate 10 near the surface of the planar inductor. This electric field, the current in the metal plate, and the planar inductor 50 generate a magnetic field between the metal plate and the planar inductor 50 in the same direction as the magnetic flux induced by the planar inductor 50. Here, the metal plate is shaped like a plate and is made of metal. The electric field generated in the dielectric substrate fluctuates with the same period as the period of the incident wave. The periodic fluctuation of the magnetic field periodically fluctuates the electric field between the thin-film conductive layer 30 and the planar inductor 50. As a result, a non-propagating, periodically fluctuating electromagnetic field is generated between the thin-film conductive layer 30 and the planar inductor 50. As will be shown later by current density simulation, an AC current is induced in the metal plate due to the magnetic field in the periodically fluctuating electromagnetic field. Furthermore, the periodically fluctuating electric field generates a periodically fluctuating potential in the metal plate. The electromagnetic field does not propagate but remains in place, and the induced AC current loses power. As a result, the energy of the electromagnetic field is converted into heat, resulting in the absorption of electromagnetic waves. Furthermore, the AC current induced in the metal plate is thought to re-emit electromagnetic waves from the surface of the metal plate opposite the surface in contact with the dielectric substrate 10. In other words, it is thought that part of the energy of the electromagnetic wave captured by the electromagnetic wave attenuation film is converted into heat energy, and the rest is re-emitted. Furthermore, according to classical electromagnetic theory, expressed in Maxwell's equations, the frequency of the induced alternating current is the same as that of the incident wave, so the frequency of the re-emitted electromagnetic wave is the same as that of the incident wave. As a result, an electromagnetic wave with the same frequency as the incident wave is re-emitted. Furthermore, if we consider an oscillating electromagnetic field as a quantum, it is possible that the quantum loses energy and re-emits a lower-energy, longer-wavelength electromagnetic wave. Re-emission can be thought of as either stimulated emission or spontaneous emission due to the incident electromagnetic wave. Stimulated emission is thought to occur when an electromagnetic wave is reflected in the direction of the incident wave, i.e., the direction of specular reflection, and a coherent electromagnetic wave is emitted. Spontaneous emission is thought to decay over time. Furthermore, the spatial distribution of spontaneous emission is thought to be close to Lambertian reflection if the electromagnetic wave attenuation film does not have a diffractive, interference, or refractive structure. The attenuation central wavelength correlates with the dimension W1 (see FIG. 7; hereinafter, sometimes referred to as "width W1") in the plane direction of the thin-film conductive layer 30 formed on the first region 121 shown in FIG. 2. That is, the wavelength of the electromagnetic wave that is suitably attenuated by the first mechanism can be changed by changing the dimension W1, and in the electromagnetic wave attenuation film 1, the attenuation of the electromagnetic wave can be set easily and with a high degree of freedom. Therefore, it is possible to easily configure the electromagnetic wave attenuation film 1 to capture linearly polarized electromagnetic waves in the band of 15 GHz or more and 150 GHz or less.

[0033] The periodic fluctuation of the non-propagating electromagnetic field is thought to occur between opposing sides of the metal plate in a planar view. Therefore, for the first mechanism to occur, it is preferable that sides of a certain length face each other. Based on this and the inventors' research results, a section of the thin-film conductive layer with a width W1 of 0.25 mm or more can be defined as a metal plate. If a metal plate can have multiple W1 values, the largest value among them can be defined as W1 for that metal plate. By setting W1 within the range of approximately 0.25 mm to 4 mm, it is possible to attenuate electromagnetic waves in the bands above 15 GHz and below 150 GHz. The relationship between the frequency of the attenuated electromagnetic wave and the width of the metal plate can be expressed as a straight line on a logarithmic graph, as shown in Figure 25. In other words, the frequency of the attenuated electromagnetic wave is a power function of the width of the metal plate. The power of this function is approximately -1, and the relationship is almost inversely proportional. The thin-film conductive layer may include a plurality of metal plates having different dimensions W1. In this case, the attenuation peaks of the respective electromagnetic waves are overlapped, thereby broadening the band of the electromagnetic waves that can be attenuated.

[0034] The second mechanism is the confinement of the electromagnetic field by the thin-film conductive layer 30 and the planar inductor 50. In the electromagnetic wave-attenuating film 1, the dielectric substrate 10 is sandwiched between the thin-film conductive layer 30 and the planar inductor 50 in the first region 121. Therefore, the electric field generated in the dielectric substrate 10 of the electromagnetic wave-attenuating film 1 by electromagnetic waves is confined within the dielectric substrate 10 between the thin-film conductive layer 30 including the metal plate and the planar inductor 50 by the charge and current in the metal plate. In other words, the metal plate suppresses the electromagnetic field and confines it within the dielectric substrate 10. In other words, the metal plate can function as a choke. In other words, the metal plate can function as a choke plate. It is also believed that magnetic flux is induced within the first region by the periodic fluctuations of this trapped electric field. This causes the oscillating electromagnetic field to accumulate within the first region, increasing the energy density of the electromagnetic field. Generally, the higher the energy density, the easier it is to attenuate, so this mechanism efficiently attenuates electromagnetic waves. Furthermore, in the second mechanism, the higher the dielectric loss tangent of the dielectric substrate 10, the greater the energy loss of the electromagnetic field accumulated within the dielectric substrate. Furthermore, the magnetic field accumulated in the dielectric substrate is accompanied by a large current in the metal plate, and the electric field accumulated in the dielectric substrate generates a large potential difference. The product of a large current and a large potential difference can increase power loss. The energy of the electromagnetic wave is consumed as power loss, resulting in attenuation of the electromagnetic wave.

[0035] The third mechanism is power loss in an electric circuit including a capacitor formed by the opposing thin-film conductive layer 30 and planar inductor 50 and the dielectric substrate 10 therebetween. In the electromagnetic wave-damping film 1, the dielectric substrate 10 is sandwiched between the thin-film conductive layer 30 and the planar inductor 50 in both the first region 121 and the second region 122. Therefore, the first region 121, the second region 122, and the dielectric substrate 10 function as a capacitor. Therefore, electromagnetic waves incident on the dielectric substrate 10 of the electromagnetic wave-damping film 1 are attenuated by the electric circuit including the capacitor. The larger the capacitance of a capacitor, the more charge it can store, thereby increasing the amount of energy it can store. Therefore, the larger the capacitance, the greater the capacity it can handle. Because capacitance is inversely proportional to the thickness of the dielectric substrate 10, a thinner dielectric substrate 10 is preferable. Furthermore, because the distance between the thin-film conductive layer 30 and the planar inductor 50 is determined by the thickness of the dielectric substrate 10, the electrical resistance between the thin-film conductive layer 30 and the planar inductor 50 is proportional to the thickness of the dielectric substrate 10. A low resistance of the dielectric substrate 10 increases leakage current in the dielectric substrate 10, increasing the current flowing in the electrical circuit including the capacitor between the thin-film conductive layer 30 and the planar inductor 50. This increases power loss due to leakage current, which in turn increases the absorption of electromagnetic wave energy. Furthermore, in the electromagnetic wave attenuation film 1 according to the embodiment of the present invention, changing the thickness of the dielectric substrate 10 at the location where the metal plate is disposed does not shift the wavelength of the attenuated electromagnetic field. Therefore, the thickness of the dielectric substrate 10 can be designed to match the characteristics of the electrical circuit including the capacitor.

[0036] As described above, electromagnetic waves incident on the electromagnetic-wave-attenuating film 1 are trapped by generating an electromagnetic field in the dielectric substrate 10 near the surface of the planar inductor through the first mechanism, and then confining the electromagnetic field generated by the electromagnetic waves through the second mechanism. In this way, the electromagnetic-wave-attenuating film 1 can trap electromagnetic waves. The trapped electromagnetic waves are attenuated by electric field loss and power loss through the second mechanism and power loss through the electrical circuit through the third mechanism. Furthermore, providing the topcoat layer 200 matches the impedance of the air through which the radio waves propagate, enabling the radio waves to be effectively attenuated by the thin-film conductive layer. The wavelength of the attenuated electromagnetic waves can be adjusted by changing the dimension W1 of the metal plate, as shown in Figure 25. More specifically, the frequency at which the reflected wave is minimized, i.e., the frequency at which attenuation is maximized, closely approximates the power of the size of the metal plate, as shown in Figure 25. Therefore, the electromagnetic-wave attenuation characteristics of the electromagnetic-wave-attenuating film 1 can be easily and flexibly set. Therefore, it is easy to set it to capture linearly polarized, circularly polarized, or elliptically polarized radio waves in the band of 15 GHz or more and 150 GHz or less. In the simulation of FIG. 25, the metal plate is square and W1 is the length of one side.

[0037] The dielectric substrate of the electromagnetic wave attenuation film 1 of the first embodiment has a first region 121 and a second region 122, and at least a part of the side surface 122a of the second region 122 is exposed without being covered by the thin-film conductive layer 30. As a result, it is possible to easily increase the area onto which electromagnetic waves can be incident without increasing the planar area of ​​the electromagnetic wave attenuation film, and to efficiently capture and attenuate electromagnetic waves.

[0038] In the electromagnetic wave attenuation film 1 of the first embodiment, the thin-film conductive layer 30 on the second region 122 that serves as the support cage improves the attenuation of electromagnetic waves mainly by enhancing the second and third mechanisms. Furthermore, the inventors' investigations have shown that the electric field is stronger at the periphery of the metal plate, and that a potential is also generated in the support cage close to the periphery.

[0039] Figure 4 shows the simulation results of the electric field strength when there is no support cage, and Figure 5 shows the simulation results when there is a support cage. In Figures 4 and 5, (a) shows the peripheral part of the metal plate, and (b) shows an enlarged view, with the metal plate labeled A and the support cage labeled B. Comparing Figure 4(b) with Figure 5(b), it can be seen that the electric field intensity is stronger at the periphery of the metal plate in Figure 5(b). In other words, the above-mentioned potential generated in the support cage is thought to contribute to the larger power loss in the first mechanism.

[0040] The third mechanism also plays an important role in the electromagnetic-wave-attenuating film 1. When an electric field is generated in the dielectric substrate 10, the electromagnetic field is confined below the metal plate. That is, an electromagnetic field with high energy density is generated below the metal plate. It is believed that the confined electromagnetic field is attenuated by power loss due to the second mechanism and dielectric loss due to the third mechanism.

[0041] The inventors' investigations revealed that the attenuation by the first mechanism changes depending on the admittance (the reciprocal of electrical resistance) of the metal that makes up the metal plate. Good electromagnetic wave attenuation was obtained when the admittance (siemens / m) was 10 million or more. Silver is known to have the highest admittance among normal conductors, with an admittance of 61 to 66 x 10 6 Therefore, the upper limit of admittance is approximately 70 million. Metals with admittances between 5 million and 70 million can be used. The metals that make up the metal plate can be ferromagnetic, paramagnetic, diamagnetic, or antiferromagnetic. Examples of ferromagnetic metals are nickel, cobalt, iron, or their alloys. Examples of paramagnetic metals are aluminum, tin (β-tin), or their alloys. Examples of diamagnetic metals are gold, silver, copper, tin (α-tin), zinc, or their alloys. An example of a diamagnetic alloy is brass, an alloy of copper and zinc. An example of an antiferromagnetic metal is chromium. Metal plates made of these metals have been shown to exhibit good electromagnetic wave attenuation. On the other hand, in the present invention, the surface of the metal plate may be oxidized, nitrided, or oxynitrided. The metal oxide or metal nitride on the surface of the metal plate can be formed by surface treatment. The surface treatment can be a chemical treatment using chemicals, a heat treatment, or both. Furthermore, the metal plate may have a metal oxide film or a layer of a mixture of metal and metal oxide. In such a configuration, the resistance value of the metal plate increases, and the voltage drop increases, resulting in increased power loss and improved electromagnetic wave attenuation. The metal plate 30A may be a multi-layer film made by laminating films made of different materials, and the materials of the laminated films may be conductive or insulating.

[0042] An example of a manufacturing procedure for the electromagnetic wave attenuation film 1 will be described. First, the dielectric substrate 10 is formed. A resin that forms the uneven portion is arranged in layers on the carrier 11, and a first region and a second region are formed on the surface, completing the dielectric substrate 10 having the underlayer 12. The resin that forms the underlayer 12 can be a photosensitive resin. In this case, photolithography can be used. The photosensitive resin can be a negative resist or a positive resist. The underlayer 12 can also be formed from a photocurable resin. The underlayer 12 can also be formed from a thermoplastic resin. In this case, thermal transfer can be used. The underlayer 12 can also be formed from a thermosetting resin. The resin may be a soluble resin that is soluble in a solvent (oil-based ink). The resin may also be a water-soluble resin (water-based ink).

[0043] Next, the thin-film conductive layer 30 and the planar inductor 50 are formed on the front surface 10a and back surface 10b of the dielectric substrate 10, respectively. The thin-film conductive layer 30 and the planar inductor 50 can be formed by physical deposition. Physical deposition can be vapor deposition or sputtering. Either the thin-film conductive layer 30 or the planar inductor 50 can be formed first, and they can be made of different materials. The planar inductor 50 can be made of any of a casting, a rolled metal plate, a metal foil, a vapor-deposited film, a sputtered film, and plating. The casting can be made of cast iron or an aluminum alloy. The rolled metal plate can be made of steel, stainless steel, aluminum, or an aluminum alloy. The plating can be electrolytic plating or electroless plating. The plating can be copper plating, electroless nickel plating, electrolytic nickel plating, zinc plating, electrolytic chromium plating, or a laminate of these. It is important that the thin-film conductive layer 30 is not connected to the metal plate and other parts. If the metal plate and other parts are connected, the width W1 described above will change, which may result in electromagnetic wave attenuation different from what was expected. For this reason, a step of removing the thin-film conductive layer 30 formed on the side surface of the second region may be added. Laser etching or the like can be used for this step.

[0044] When providing the top coat layer 200, the coating method is not particularly limited and may be appropriately selected from methods used in film production. Examples of the coating method include gravure coating, reverse coating, gravure reverse coating, die coating, and flow coating.

[0045] In the above-described manufacturing procedure, the carrier 11 may be peeled off after forming the underlayer 12. In this way, a single-layer dielectric substrate consisting of only the underlayer 12 is formed.

[0046] As another example of a manufacturing procedure, after forming the thin-film conductive layer 30 and the planar inductor 50 on the dielectric substrate, a concave-convex shape may be formed on the thin-film conductive layer 30. In this case, transfer using a plate is preferable. When performing thermal transfer, the plate is pressed against the thin-film conductive layer 30 and heated. In this manufacturing procedure, the thin-film conductive layer 30 pressed against the plate tends to stretch, resulting in a state in which the metal plate is connected to the other parts. Methods to resolve this include the laser etching described above, as well as devising the shape of the plate. For example, if the edges of the convex portions that form the first region on the plate are sharpened, the edges of the metal plate are cut when the plate is pressed against the thin-film conductive layer 30. This ensures that the metal plate is not connected to the other parts during transfer.

[0047] A second embodiment of the present invention will be described with reference to Figures 6 to 9. In the following description, components common to those already described will be assigned the same reference numerals, and duplicated descriptions will be omitted. It is believed that the first, second, and third mechanisms described above are also realized in the second embodiment.

[0048] An electromagnetic-wave attenuation film 61 according to a second embodiment is shown in Fig. 6 and Fig. 7. Fig. 6 is a schematic plan view showing an electromagnetic-wave attenuation film according to a second embodiment of the present invention, and Fig. 7 is a schematic view showing a part of a cross section taken along line II-II in Fig. 6. Fig. 8 is a schematic view showing a part of a cross section taken along line II-II in Fig. 6 when a top coat layer is provided. The electromagnetic wave attenuation film 61 includes a dielectric substrate 62, a plurality of metal plates 30A, and a planar inductor 50. The thickness of the metal plates 30A can be 1000 nm or less.

[0049] The dielectric substrate 62 of the second embodiment can be made of the same material and structure as the dielectric substrate of the first embodiment. The dielectric substrate 62 can be configured with a base layer provided on the carrier 11, or it can be configured with only the carrier 11. Both the front surface 62a and the back surface 62b are flat or rough. The back surface 62b is provided with a planar inductor 50, and an adhesive layer may be provided between the back surface 62b and the planar inductor 50. The adhesive layer and the planar inductor 50 can be formed using the same materials and manufacturing methods as in the first embodiment. Multiple metal plates 30A are disposed on the front surface 62a. The metal plates 30A can be formed by deposition followed by etching. This deposition method can be physical deposition or chemical deposition. Physical deposition is suitable for forming the metal plates. Physical deposition can be vacuum deposition or sputtering. Vacuum deposition is preferred due to its high productivity. Metal plates can be formed by printing a mask layer in the shape of the metal plates and then removing the excess thin-film conductive layer by etching. The etching solution used for etching can be a sodium hydroxide solution. The concentration of the sodium hydroxide solution can be 0.001 mol / L or more and 1 mol / L or less. The metal of the metal plate 30A can be the same metal as in the first embodiment. The metal plates are arranged discretely. The attenuation center frequency can be expressed as a power function of the width of the metal plate. The multiple metal plates 30A may be of the same shape and size and arranged at regular intervals. In other words, two or more multiple metal plates 30A of the same shape and size may be arranged at regular intervals. In other words, the front surface 62a is not entirely covered with a metal layer, and the dielectric substrate 62 is exposed in areas where the metal plates 30A are not arranged.

[0050] Furthermore, multiple metal plates 30A of the same shape and size as each of the multiple metal plates 30A may be arranged among multiple metal plates 30A of different shapes, sizes, or both. In other words, multiple metal plates of different shapes, sizes, or both may be arranged, or multiple metal plates of the same shape and size may be arranged. The metal plates may be arranged at regular intervals and in a regular orientation. Alternatively, they may be arranged at different intervals and in different orientations. Furthermore, they may be arranged at different intervals and in the same orientation. Furthermore, multiple metal plates of different shapes, sizes, or both may be grouped into a metal plate set. The spacing between the metal plates constituting the metal plate set may be all or some of the same, or all of the different. The orientations of the metal plates constituting the metal plate set may be all or some of the same, or all of the different. A metal plate set having multiple metal plates of different shapes, sizes, or both may have different attenuation frequency spectra, allowing for attenuation of multiple frequency bands or a broadband of attenuated frequencies. Furthermore, different spacing between the metal plates can result in different attenuation frequency spectra. Different orientations of the metal plate sets can result in different polarization dependence of attenuation. The multiple metal plates that make up a metal plate set can each attenuate different frequencies, and the frequency differences can be regular. Multiple metal plate sets may be arranged. Multiple metal plate sets may be arranged, each consisting of metal plates with the same shape, size, and arrangement as the metal plates constituting a given metal plate set. By including multiple different metal plates in the thin-film conductive layer, it is possible to broaden the bandwidth, attenuate electromagnetic waves of multiple frequencies, or both.

[0051] The metal plate may be divided into multiple metal segments. In other words, the metal plate may be composed of multiple metal segments. The multiple metal segments within the metal plate may be electrically connected. The multiple metal segments may be electrically connected by wiring. The wiring may have an impedance. This impedance may be matched to the metal segments. The wiring and the multiple metal segments within the metal plate may function as a single unit. The multiple metal segments may have different properties than when they exist alone. Specifically, the resonant frequency and attenuation may be different when they exist alone than when they form part of the metal plate. The cross-sectional shape of the metal plate may be flat, polyhedral, or curved. In the case of a polyhedron or curved shape, the distance between the base and the apex, i.e., the height, may be 50 μm or less. The ratio of the height to the distance between the opposing sides of the metal plate may be 1:100 or more and 1:10 or less.

[0052] The attenuation of the electromagnetic wave attenuation film of the second embodiment can be adjusted by changing the width W1 of the metal plate, as in the first embodiment, and it is also easy to set it to capture linearly polarized electromagnetic waves in the band between 15 GHz and 150 GHz. Furthermore, since the plastic film carrier 11 can be used as the dielectric substrate 62 as is, the electromagnetic wave attenuation film of the second embodiment can be produced more easily than the electromagnetic wave attenuation film of the first embodiment. A carrier having a roughened surface on part or the entire surface of the front surface 62a and the back surface 62b can also be used as the dielectric substrate 62. By roughening part or the entire surface of the front surface 62a, the admittance of the metal plate 30A can be adjusted.

[0053] In prior art including Patent Document 5, it was believed that making the resonating conductor thicker than the skin depth would generate a sufficient AC current in the resonant layer, and that the power loss of that AC current would attenuate electromagnetic waves. However, the inventors discovered that when the thickness of the metal plate 30A is equal to or less than the skin depth, the attenuation of electromagnetic waves actually increases.

[0054] Figure 9 shows the results of a simulation of the electromagnetic wave attenuation due to changes in the thickness of the metal plate 30A. The metal plate is made of aluminum. The incident wave is a linearly polarized sine wave that is incident perpendicularly to the electromagnetic wave attenuation film. In the simulation, the planar inductor is considered a perfect conductor. The electromagnetic wave attenuation of the electromagnetic wave attenuation film is measured using the monostatic RCS, which is based on the case where only the planar inductor is used. The vertical axis showing the electromagnetic wave attenuation is expressed in decibels. Monostatic RCS (Radar Cross-Section) is an index that indicates the ease of target detection by monostatic radar, and can be calculated using the following equation 1. Monostatic radar transmits and receives signals at the same location.

[0055]

number

[0056] As a result of the simulation, significant attenuation of electromagnetic waves was observed when the thickness was 40 nm or more and 400 nm or less, as shown in Figure 9. Conversely, when the thickness was less than 40 nm, a decrease in attenuation of electromagnetic waves was observed. In addition, when the metal plate 30A includes a conductive layer and a clad, stable film formation is possible if the thickness of the metal plate 30A including the conductive layer and the clad is 1000 nm or less.

[0057] The phenomenon shown in Figure 9 shows an interesting relationship with the skin depth. The skin depth of aluminum at a frequency of 41 GHz is approximately 400 nm. In other words, when the thickness of the metal plate becomes less than the skin depth of the material, the attenuation of the electromagnetic wave increases. Also, 1 / e of the skin depth 2 When the thickness of the conductive layer is less than the skin depth, the attenuation of the electromagnetic wave decreases. This is because, if the conductive layer is thicker than the skin depth, there is insufficient resistance and the voltage drop required for power loss is not obtained, and the current is concentrated only near the center of the metal plate, reducing the current in the area where the potential difference is generated. On the other hand, even if the thickness of the conductive layer is less than the skin depth, the attenuation of the electromagnetic wave decreases when the thickness is less than 1 / e of the skin depth. 2If the voltage is less than this, it is thought that there will not be enough current to compensate for the power loss. Needless to say, power loss is given as the product of current and voltage. In other words, it can be said that sufficient electromagnetic wave attenuation will be achieved as long as the following LN function equation 2, which is expressed using the natural logarithm of the metal plate thickness T normalized by the skin depth d, is satisfied. -2 ≦ ln(T / d) ≦ 0 …(2) Furthermore, when a metal with low admittance is used for the metal plate, electromagnetic wave attenuation can be obtained even within the range of the following formula 3. Furthermore, when the area of ​​the metal plate occupies a large proportion of the front surface of the dielectric substrate, electromagnetic wave attenuation can be obtained even within the range of the following formula 3. When this area ratio is large, the proportion of the area of ​​the metal plate occupying the front surface of the dielectric substrate can be 50% or more and 90% or less. 0 < ln(T / d) ≦ 1 …(3) Considering the formulas 1 and 2, the attenuation of the electromagnetic wave can be obtained within the range of the following formula 4. -2 ≦ ln(T / d) ≦ 1 …(4) In the embodiment of the present invention, the skin depth can be calculated using the attenuation center frequency f. That is, when the attenuation center frequency f is used, the skin depth d is calculated as shown in the following equation 5, as is well known.

[0058]

number

[0059] Furthermore, the simulation results showed that attenuation increased when the thickness of the metal plate was thinner than the skin depth. This is thought to be because the current generated by the magnetic flux in the dielectric substrate of the metal plate reaches the opposite surface of the dielectric substrate, and this current emits electromagnetic waves that are π-phase-shifted from the reflected waves by the dielectric inductor, canceling out the reflected waves. Furthermore, as the thickness of the metal plate becomes thinner than the skin depth, the current in the metal plate is restricted, causing the magnetic field to be generated not only near the center of the metal plate but throughout the entire metal plate. This in turn causes the current induced by the generated magnetic field to be generated throughout the entire metal plate, increasing the emission of electromagnetic waves that cancel out the reflected waves by the dielectric inductor, resulting in greater attenuation of the reflected waves. In addition, the electric field of the dielectric substrate between the metal plate and the dielectric inductor attracts the metal plate and the dielectric inductor. If the electric field fluctuates periodically, the force of attraction to the metal plate also fluctuates periodically. Therefore, the electric field of the dielectric substrate between the metal plate and the dielectric inductor causes the metal plate to vibrate. The energy of this vibration is converted into heat and lost. For this reason, it is thought that the mechanics of the electromagnetic field acting on the metal plate also contributes to the attenuation of electromagnetic waves. Furthermore, if we consider the non-propagating periodic fluctuations of the electromagnetic field as quanta, we can think of it as a state in which the quantum is trapped by the electromagnetic field with zero momentum. In addition, since the thickness of the metal plate is on the order of several hundred nanometers, it is possible that this may affect the energy levels within the metal plate. Thus, the phenomena in the embodiments of the present invention can be interpreted not only as classical electromagnetic phenomena, but also as classical mechanics and quantum mechanics. Therefore, when interpreting Equation 4, the range is reasonably defined, but it is not a range that is strictly calculated taking into account all physical phenomena. Therefore, when determining whether a product falls within the range of the above formula, it is appropriate to interpret it taking into account the physical phenomena that are manifesting. In the prior art, it is not common to see examples of using a conductor that is approximately skin depth or thinner than the skin depth. Therefore, it is believed that the mechanism of interaction between the embodiment of the present invention and electromagnetic waves in the millimeter wave band is different from the prior art.

[0060] The relationship between the thickness of the metal plate and the skin depth that exhibits preferable electromagnetic wave attenuation for a specific frequency band will be described in detail in an example according to the second embodiment, which will be described later.

[0061] Each embodiment of the present invention will be further described using examples. (Example according to the first embodiment) First, a master plate for nickel electroforming was prepared. A resist pattern was formed on the surface of a silicon wafer by photolithography. The photoresist used was a positive type, and the thickness of the photoresist was 10 μm. The formed resist pattern was a pattern in which square openings were arranged in a square area with sides of 14 cm in an XY coordinate system at coordinates that formed a square lattice array with a constant period in both the X and Y coordinates, and the area exposed to i-line light was the area inside the square. Furthermore, nickel electroforming was carried out using this master plate to obtain a nickel mold having a pattern in which square convex portions in a plan view were regularly arranged on the surface.

[0062] Next, UV-curable resin was dropped onto the patterned surface of the nickel mold, and the adhesive side of a PET film with an adhesive treatment on one side was placed on top of the UV-curable resin. The UV-curable resin was spread evenly over the patterned surface using a roller, and then irradiated with UV light through the transparent PET film to cure the UV-curable resin. The PET film was released from the nickel mold to obtain a dielectric part consisting of the PET film and the irregular layer made of the ultraviolet curable resin.

[0063] A 500 nm thick Al film was formed on both sides of the dielectric substrate by vacuum deposition to form a thin film conductive layer and a planar inductor. The above is the manufacturing procedure for the examples according to the first embodiment. In this procedure, a plurality of nickel molds were produced with different parameters for the concave-convex layer surface, and the electromagnetic wave attenuation films of Examples 1 and 2 were produced. The electromagnetic wave attenuation films according to the respective examples were thin and lightweight, with a thickness of about 60 μm and a weight of about 0.02 g.

[0064] (Modification in which a top coat layer is provided in the example according to the first embodiment) In the example according to the first embodiment, an electromagnetic wave attenuation film was prepared by providing a top coat layer 200 manufactured in the following manner. The main component is an acrylic resin composition consisting of a mixture of 80 parts by mass of methyl methacrylate monomer and 20 parts by mass of cyclohexyl methacrylate, and the solid content of the acrylic resin composition is 100 parts by mass. The composition further contains 6 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber having the structure shown in Chemical Formula A above ("ADEKA STAB LA-46" manufactured by ADEKA CORPORATION), 6 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber having a different composition from the structure shown in Chemical Formula A above ("TINUVIN 479" manufactured by Chiba Specialty Chemicals Co., Ltd.), 3 parts by mass of a benzotriazole-based ultraviolet absorber ("TINUVIN 329" manufactured by Chiba Specialty Chemicals Co., Ltd.), and A base solution with a solids content of 33 parts by weight, containing 5 parts by weight of a hindered amine radical scavenger (Ciba Specialty Chemicals' "Tinuvin 292") and 75 parts by weight of a hexamethylene diisocyanate curing agent solution with ethyl acetate added to adjust the solids content, was mixed at a ratio of 10:1 (the ratio of hydroxyl groups in the base solution to isocyanate groups in the curing agent solution was 1:2), and ethyl acetate was added as a solvent to adjust the solids content to 20 parts by weight. The resulting coating solution was applied to a thickness of 6 μm after solvent evaporation, yielding a topcoat layer 200. The resulting electromagnetic wave-attenuating film was thin and lightweight, measuring approximately 70 μm in thickness and weighing approximately 0.02 g.

[0065] (Example according to the second embodiment) [57GHz~90GHz] Example 1A In contrast to the general theory stated in Equation 4, we have been able to find a range of the relationship ln(T / d) between the metal plate thickness T and the skin depth d that shows favorable electromagnetic wave attenuation in a specific frequency band within the millimeter wave band, which is explained below. We will explain the simulations carried out in the 57GHz to 90GHz band. The dielectric substrate was a PET film with a thickness (H1) of 50μm, and on one side of it, metal plates with thin-film conductive layers were set at regular intervals in both the X and Y coordinates. Furthermore, on the other side of the dielectric substrate, an aluminum plate inductor with a thickness (T2) of approximately 2mm was set, and the simulation was carried out. Simulations were performed on the relationship between electromagnetic wave attenuation and ln(T1 / d) for each metal type at frequencies of 57 GHz, 66 GHz, 71 GHz, 81 GHz, 86 GHz, and 90 GHz.

[0066] The simulation results are explained in Tables 1 and 2 and Figs. 10 to 15. Fig. 10 is a graph showing the electromagnetic wave attenuation characteristics of Example 1A at 57 GHz. Fig. 11 is a graph showing the electromagnetic wave attenuation characteristics of Example 1A at 66 GHz. Fig. 12 is a graph showing the electromagnetic wave attenuation characteristics of Example 1A at 71 GHz. Fig. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 1A at 81 GHz. Fig. 14 is a graph showing the electromagnetic wave attenuation characteristics of Example 1A at 86 GHz. Fig. 15 is a graph showing the electromagnetic wave attenuation characteristics of Example 1A at 90 GHz. In Figs. 10 to 15, (a) shows the admittance and skin depth values, (b) shows the configuration of the electromagnetic wave attenuation film, and (c) to (e) show graphs of the attenuation characteristics of silver, copper, and aluminum, respectively. The graph shows the correlation between the thickness T1 of the metal plate normalized by the skin depth d on the horizontal axis and the attenuation of the patterned metal plate when the reflection amount of a metal plate with the same area as the dielectric substrate is set to 100 (reference) on the vertical axis. [Table 1] [Table 2]

[0067] If an electromagnetic wave attenuation film has an absorption of 10 dB or more as a guideline for a good attenuation amount, then as is clear from Table 1 and Figs. 10 to 15, it was shown that in the frequency band of 57 GHz to 90 GHz, films that satisfy -2.5 ≦ ln(T1 / d) ≦ -1.0 can obtain a good attenuation amount. It should be noted that a satisfactory attenuation characteristic of about 10 dB is not limited to the numerical values ​​of the parameters used in Example 1A, and it can be expected that it can be realized in a configuration with a certain range. For example, a satisfactory attenuation characteristic of about 10 dB can be expected even in a configuration in which the width W1 of the metal plates is 0.9 mm to 1.4 mm, the distance W3 between adjacent metal plates is 0.5 mm to 0.7 mm, the thickness H1 of the dielectric substrate is 5 μm to 300 μm, and the thickness T2 of the planar inductor is 0.5 μm to 5 mm.

[0068] Example 1B As in Example 1A, the dielectric substrate was a PET film with a thickness (H1) of 50 μm, and the ratio of the total area of ​​the metal plate, a thin-film conductive layer, to the total area of ​​the dielectric substrate in the XY plane was varied. Furthermore, an aluminum plate inductor with a thickness (T2) of approximately 2 mm was set on the other side of the dielectric substrate, and simulations were performed. The metal plate was made of aluminum, with a width W1 of 1.0 mm and a thickness T1 of 80 nm. The ratio of the metal area was changed by adjusting the distance W3 between the metal plates. The simulation results are explained in Table 3 and Fig. 16. Fig. 16 is a graph showing the electromagnetic wave attenuation characteristics as a function of the metal area ratio at 81 GHz for Example 1B. (a) shows the configuration of the electromagnetic wave attenuation film, and (b) shows the attenuation characteristics. [Table 3] If an absorption of 10 dB or more by an electromagnetic wave attenuation film is considered to be a good attenuation level, Table 3 and FIG. 16 show that in Example 1B, a good attenuation level can be obtained when the metal area ratio is around 10 to 40%.

[0069] Example 1C As in Example 1A, a 50 μm thick (H1) PET film was used as the dielectric substrate, and a metal plate, a thin-film conductive layer, was arranged on one side of the film in the same pattern as in Figure 6, but the shape was changed to a shape other than square.Furthermore, an aluminum plate inductor with a thickness (T2) of approximately 2 mm was set on the other side of the dielectric substrate, and the electromagnetic wave attenuation characteristics were simulated.Aluminum was used as the metal type for the metal plate, and the thickness T1 was set to 80 nm.

[0070] [Rectangular shape] Figure 17 is a graph showing the electromagnetic wave attenuation characteristics of the rectangular metal plate in Example 1C. (a) shows the shape of the metal plate, with W7 representing the length of the long side of the rectangle and W8 representing the length of the short side. (b) is an enlarged view of a portion of the arrangement pattern in this example, passing through line II-II in Figure 6, in which W4 represents the distance between the centers of the rectangles. (c) shows the dimensions of W7, W8, and W4. (d) shows the attenuation characteristics with frequency on the horizontal axis. The simulation results showed good attenuation characteristics with an absorption of 10 dB or more around 82.8 GHz.

[0071] [Hexagonal shape] Figure 18 is a graph showing the electromagnetic wave attenuation characteristics of the hexagonal metal plate in Example 1C. (a) shows the shape of the metal plate, with W9 representing the length of one side of the hexagon. (b) is an enlarged view of a portion of the arrangement pattern in this example, passing through line II-II in Figure 6, in the vicinity of which W4 represents the distance between the centers of the hexagons. (c) shows the dimensions of W9 and W4. (d) shows the attenuation characteristics with frequency on the horizontal axis. The simulation results showed good attenuation characteristics with an absorption of 10 dB or more around 71.2 GHz.

[0072] [Convex shape] Figure 19 is a graph showing the electromagnetic wave attenuation characteristics of the convex metal plate in Example 1C. (a) shows the shape of the metal plate. W10 represents the length of the upper edge of the convex upper portion, W11 represents the length of the lower edge of the convex lower portion, W15 represents the length of the side edge of the upper portion, and W16 represents the length of the side edge of the lower portion. The convex shape is symmetrical with respect to the line connecting the midpoint of the upper edge of the upper portion and the lower edge of the lower portion. The center of the convex shape is the center of a rectangle that is tangent to the lower edge of the lower portion, the left and right sides of the lower portion, and the upper edge of the upper portion and surrounds the convex shape. (b) is an enlarged view of the vicinity of the arrangement pattern passing through line II-II in Figure 6 in this example, where W4 represents the distance between the centers of the convex shapes. (c) shows the dimensions W10, W11, W15, W16, and W4. (d) shows the attenuation characteristics with frequency as the horizontal axis. The simulation results showed good attenuation characteristics with an absorption of 10 dB or more around 87 GHz.

[0073] [Triangular shape] Figure 20 is a graph showing the electromagnetic wave attenuation characteristics of the triangular metal plate in Example 1C. (a) shows the shape of the metal plate, where W12 represents the length of one side of the equilateral triangle. (b) is an enlarged view of a portion of the arrangement pattern in this example, passing through line II-II in Figure 6, in which W4 represents the distance between the centers of the triangles. (c) shows the dimensions of W12 and W4. (d) shows the attenuation characteristics with frequency on the horizontal axis. The simulation results showed good attenuation characteristics with an absorption of 10 dB or more around 80.8 GHz.

[0074] [Cross shape] FIG. 21 is a graph showing the electromagnetic wave attenuation characteristics of a cross-shaped metal plate in Example 1C. (a) shows the shape of the metal plate. The cross shape is symmetrical vertically and horizontally, and is also symmetrical with respect to a 90-degree rotation. W13 represents the length of the opposing outer edges of the cross, and W14 represents the length of one side of a square that contacts the opposing outer edges and surrounds the cross. The center of the square is the center of the cross. (b) is an enlarged view of a portion of the arrangement pattern in this example, passing through line II-II in FIG. 6, and W4 represents the distance between the centers of the cross shapes. (c) shows the dimensions W13, W14, and W4. (d) shows the attenuation characteristics with frequency as the horizontal axis. The simulation results showed good attenuation characteristics with an absorption of 10 dB or more around 90 GHz.

[0075] Example 2 A square PET film with a thickness of 50 μm and sides of 14 cm was prepared as the dielectric substrate. A 100 nm thick thin-film conductive layer of aluminum was formed on the entire surface of one side of the dielectric substrate using vacuum deposition. The thin-film conductive layer was then etched using a mask to form a metal plate at a fixed interval in both the X and Y coordinates. An aluminum flat inductor was attached to the other side using an adhesive layer. Simulations were also performed using this configuration. The above is the manufacturing procedure for Example 2 according to the second embodiment. The parameters for Example 2 are as follows. Metal plate width W1: Sixteen types of metal plates with widths obtained by dividing the range of 1.025 mm to 0.9 mm into 16 equal parts at 0.083 mm intervals were arranged in a 4 x 4 matrix with the same spacing of 0.1 mm and the same orientation to form a metal plate set. Multiple such metal plate sets were arranged with spacing of 0.1 mm and the same orientation. Each metal plate set was also identical. In other words, there was no difference between the metal plates constituting each metal plate set. Distance between adjacent metal plates W3: 0.1 mm Metal plate thickness T1: 80nm Thickness of the flat inductor T2: approx. 2 mm Dielectric substrate thickness H1: 50 μm In addition, a simulation was performed using this configuration to examine the validity of the damping mechanism based on the experimental results.

[0076] The electromagnetic wave attenuation films according to the examples, which did not include a planar inductor, were thin and lightweight, measuring approximately 60 μm in thickness and weighing approximately 0.02 g. Therefore, they can be easily attached to components, such as those inside the housings of mobile phones and automotive radars, where the effects of electromagnetic radiation noise must be suppressed. In the simulation, all of Examples 1A to 1C and 2 showed good attenuation of millimeter-wave electromagnetic waves. Furthermore, actual measurements yielded attenuation rates, confirming the effectiveness of this configuration. Although there were differences between the simulation and experimental results, which are thought to be due to various parameters in the simulation and influences other than attenuation based on Maxwell's equations, similar attenuation trends were observed, and therefore the mechanism of the embodiments of the present invention is considered to be valid. Furthermore, although there were differences in the attenuation rates between the simulation and actual measurements, similar trends were obtained, demonstrating that the attenuation center frequency can be set appropriately. The monostatic RCS attenuation characteristics of the simulation results and actual measurement results for Examples 1A and 2 are shown in Figures 22 and 23, respectively. Example 1A used aluminum with a metal plate width W1 of 1.0 mm, a distance W3 between adjacent metal plates of 0.5 mm, and a metal plate thickness T1 of 100 nm. The actual measurement procedure was as follows. Two metal plates of the same dimensions were prepared, and one of them was completely covered with the electromagnetic wave attenuation film of each example. In an anechoic chamber, radio waves were irradiated onto the metal plate with the electromagnetic wave attenuation film attached and the metal plate without the film attached, and the amount of reflected radio waves was measured using a network analyzer (Keysight Model E5071C). The monostatic RCS attenuation was evaluated by setting the reflection amount of the metal plate without the electromagnetic wave attenuation film attached as 100 (reference).

[0077] (A modified example in which a top coat layer is provided in Example 1A according to the second embodiment) In Example 1A according to the second embodiment, aluminum was used, and the metal plate had a thickness T1 of 80 nm, and a top coat layer 200 manufactured by the following procedure was provided on the metal plate to produce an electromagnetic wave attenuation film. The main component is an acrylic resin composition consisting of a mixture of 80 parts by mass of methyl methacrylate monomer and 20 parts by mass of cyclohexyl methacrylate, and the solid content of the acrylic resin composition is 100 parts by mass. The composition further contains 6 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber having the structure shown in Chemical Formula A above ("ADEKA STAB LA-46" manufactured by ADEKA CORPORATION), 6 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber having a different composition from the structure shown in Chemical Formula A above ("TINUVIN 479" manufactured by Chiba Specialty Chemicals Co., Ltd.), 3 parts by mass of a benzotriazole-based ultraviolet absorber ("TINUVIN 329" manufactured by Chiba Specialty Chemicals Co., Ltd.), and A base solution with a solids content of 33 parts by weight, to which 5 parts by weight of a hindered amine radical scavenger (Ciba Specialty Chemicals' "Tinuvin 292") had been added, and ethyl acetate solvent had been added to adjust the solids content, was mixed with a hexamethylene diisocyanate-type curing agent solution with a solids content of 75 parts by weight, to which ethyl acetate solvent had been added, at a ratio of 10:1 (the ratio of hydroxyl groups in the base solution to the isocyanate groups in the curing agent solution was 1:2). Ethyl acetate was added as a solvent component to adjust the solids content to 20 parts by weight, and the resulting coating solution was applied to a thickness of 6 μm after solvent evaporation, yielding a topcoat layer 200. The topcoat layer thickness was 6 μm.

[0078] (Comparative Example 1) An electromagnetic wave attenuation film was prepared in accordance with Example 1A, without providing a topcoat layer. Furthermore, the electromagnetic wave attenuation films obtained in the above-mentioned modified examples and Comparative Example 1 were pressed onto a stainless steel plate via an adhesive, and exposed to a temperature equivalent to 10 years of outdoor exposure using a sunshine weather meter. After that, the surface of the electromagnetic wave attenuation film was wiped with a cotton cloth to examine the remaining state of the topcoat layer and the electromagnetic wave attenuation layer, and the changes in the monostatic RCS attenuation characteristics. As a result, it was confirmed that in the modified configuration, there was no deterioration in either the top coat layer or the electromagnetic wave attenuation layer, and that the formation of the top coat layer resulted in impedance matching and improved monostatic RCS attenuation characteristics, as shown in Figure 24.

[0079] Although each embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and configuration changes and combinations within the scope of the gist of the present invention are also included. Some examples of changes are shown below, but these are not all inclusive, and other changes are also possible. Two or more of these changes may be combined as appropriate.

[0080] In the first embodiment, the aspects used in the second embodiment, such as the frequency band and the metal type of the metal plate, can be used as appropriate.

[0081] In the first embodiment, the metal layer in the second region may be omitted, and only the metal plate may be formed.

[0082] In the present invention, the mode of the planar inductor is not limited to that formed on the entire rear surface. For example, a plurality of metal plates may be arranged as on the front surface, or may be in a lattice pattern.

[0083] In the present invention, the shape of the metal plate is not limited to a square, but can be set to various shapes such as a circle (including an oval), a polygon other than a square, various polygons with rounded corners, and an irregular shape. The total area of ​​the metal plates in the projected area of ​​the front surface is preferably 20% or more. In this way, electromagnetic waves can be efficiently attenuated.

[0084] The electromagnetic wave attenuation film according to the present invention can be used by laminating a plurality of sheets. By varying the structural parameters of the sheets to be laminated, it becomes possible to adjust the attenuation properties in more detail.

[0085] In the first embodiment, the heights of the first and second regions may be reversed, with the metal plate being at a relatively high position and the support cage being at a relatively low position.

[0086] The electromagnetic wave attenuation film according to the present invention may have a configuration in which a planar inductor is not provided on the back surface. For example, if the object to which the back surface is bonded is a metal, the second and third mechanisms can be exerted without any problems by the metal surface of the object to be bonded, even without a planar inductor. In such a case, it is sufficient to provide an attachment layer, such as an adhesive layer, on the back surface that can be bonded to the object.

[0087] In the electromagnetic wave attenuation film of the present invention, parameters such as the structural period and the dimensions of the metal plates do not necessarily have to be completely consistent at all locations. For example, even if the above parameters vary within the tolerance range in the manufacturing process (generally within a range of 5% or so), this also falls under the category of "same shape and same size" in the present invention. Furthermore, the "predetermined range of values" can be a regular range of values. This regularity can be a Gaussian distribution, a binomial distribution, a random or pseudo-random distribution with equal frequency within a certain area, or the range of tolerance in the manufacturing process.

[0088] The support cage may be made up of multiple conductive segments arranged with a gap between them. In this case, the gap can be 1 / 10 or less of the wavelength of the electromagnetic waves to be captured. The support cage can be made up of multiple conductive segments. In other words, the support cage may be made up of multiple conductive segments.

[0089] In the electromagnetic wave attenuation film according to the present invention, a release layer may be provided on a supporting substrate, followed by the electromagnetic wave attenuation film of the first or second embodiment, and then an adhesive, pressure sensitive adhesive, etc. may be provided to form a transfer foil. Specifically, a release layer is applied and dried on a support substrate, and then a base layer is provided on top of it. In the configuration of the first embodiment, an unevenness is imparted to the base layer, and a thin-film conductive layer is provided by vapor deposition. Then, the thin-film conductive layer formed on the side of the second region is removed, and a layer that will become the dielectric substrate is provided. A transfer foil can be obtained by laminating a flat inductor and an adhesive in this order on the dielectric substrate. In the configuration of the second embodiment, a thin-film conductive layer is provided on the base layer, and a mask layer is printed with a pattern in the shape of the metal plate. Then, excess thin-film conductive layer is removed by etching, resulting in a metal plate. Furthermore, a transfer foil can be obtained by laminating a dielectric substrate, a flat inductor, and an adhesive in this order. When transferring to a metal housing or the like, the flat inductor layer may be omitted. By using it as a transfer foil, it is possible to make the film even thinner, improve its conformability, and transfer it to complex shapes, thereby broadening the range of application of the electromagnetic wave attenuation film of the present invention.

[0090] According to the above-described embodiments and modifications, the following notes can be derived. [Appendix 1] a dielectric substrate having a front surface and a back surface; a thin film conductive layer disposed on the front surface; a flat inductor or a lamination layer disposed on the back surface; Equipped with the thin film conductive layer includes a plurality of metal plates; The thickness T of the metal plate is 1000 nm or less; Electromagnetic wave attenuation film. [Appendix 2] a dielectric substrate having a front surface and a back surface; a thin film conductive layer disposed on the front surface; a flat inductor or a lamination layer disposed on the back surface; Equipped with the thin film conductive layer includes a plurality of metal plates; When the thickness of the metal plate is T and the skin depth is d, the following formula (2) is satisfied: Electromagnetic wave attenuation film. -2 ≦ ln(T / d) ≦ 0 …(2) [Appendix 3] a dielectric substrate having a front surface and a back surface; a thin film conductive layer disposed on the front surface; a flat inductor or a lamination layer disposed on the back surface; Equipped with the thin film conductive layer includes a plurality of metal plates; The dielectric layer has a first region of a relatively low recessed portion and a second region of a relatively high recessed portion on the front surface. and a surface roughness formed by a region, The first regions are arranged discretely, the second region is disposed between a plurality of the first regions, the metal plate is disposed in the first region; When the thickness of the metal plate is T and the skin depth is d, the following formula (2) is satisfied: Electromagnetic wave attenuation film. -2 ≦ ln(T / d) ≦ 0 …(2) [Appendix 4] a dielectric substrate having a front surface and a back surface; a thin film conductive layer disposed on the front surface; a flat inductor or a lamination layer disposed on the back surface; Equipped with The dielectric layer has a first region of a relatively low recessed portion and a second region of a relatively high recessed portion on the front surface. and a surface roughness formed by a region, The thin film conductive layer includes a plurality of metal plates disposed in the first region and a plurality of metal plates disposed in the first region. and a support cage disposed thereon, The first regions are arranged discretely, The second region is disposed between a plurality of the first regions. Electromagnetic wave attenuation film.

[0091] In the above examples, we have examined the attenuation of electromagnetic waves. However, it is known that conductors that attenuate specific electromagnetic waves can be used as antennas for receiving radio waves. Therefore, the above-described embodiments can also be used as receiving antennas. Furthermore, since the above-described embodiments capture quanta with zero momentum in a two-dimensional system, it is believed that they can also be used as elements that perform data calculations and recording in the quantum state of metal plates.

[0092] As described above, the mechanism of interaction with electromagnetic waves in the embodiments of the present invention is different from that of the prior art, and therefore, any product that exhibits an equivalent mechanism should be considered to be a product that substantially employs the embodiments of the present invention. [Explanation of symbols]

[0093] 1, 61 Electromagnetic wave attenuation film 10, 62 Dielectric substrate 10a, 62a front 10b, 62b back 30 Thin film conductive layer 30A Metal Plate 50 Planar inductor 200 top coat layers 121 First area 122 Second area

Claims

1. a dielectric substrate having a front surface and a back surface; a thin film conductive layer disposed on the front surface; a planar inductor disposed on the back surface; Equipped with the thin film conductive layer includes a plurality of metal plates; The metal plates are arranged discretely, The metal plate has a polygonal, circular, or elliptical shape, When the thickness of the metal plate is T and the skin depth is d, the following formula (1) is satisfied: Electromagnetic wave attenuation film for use in the frequency range of 57 GHz to 90 GHz. -2.5 ≦ ln(T / d) ≦ -1.0...(1)

2. a dielectric substrate having a front surface and a back surface; a thin film conductive layer disposed on the front surface; a planar inductor disposed on the back surface; Equipped with the dielectric substrate has, on the front surface, an unevenness consisting of a first region of a relatively low concave portion and a second region of a relatively high concave portion; the thin-film conductive layer includes a plurality of metal plates disposed in the first region and formed on the upper surface of the second region; The first regions are arranged discretely, The metal plate has a polygonal, circular, or elliptical shape, The second region is disposed between a plurality of the first regions. Electromagnetic wave attenuation film for use in the frequency range of 57 GHz to 90 GHz.

3. a dielectric substrate having a front surface and a back surface; a thin film conductive layer disposed on the front surface; an adhesive layer disposed on the rear surface; Equipped with the thin film conductive layer includes a plurality of metal plates; The metal plates are arranged discretely, The metal plate has a polygonal, circular, or elliptical shape, When the thickness of the metal plate is T and the skin depth is d, the following formula (1) is satisfied: Electromagnetic wave attenuation film for use in the frequency range of 57 GHz to 90 GHz. -2.5 ≦ ln(T / d) ≦ -1.0...(1)

4. a dielectric substrate having a front surface and a back surface; a thin film conductive layer disposed on the front surface; an adhesive layer disposed on the rear surface; Equipped with the dielectric substrate has, on the front surface, an unevenness consisting of a first region of a relatively low concave portion and a second region of a relatively high concave portion; the thin-film conductive layer includes a plurality of metal plates disposed in the first region and formed on the upper surface of the second region; The first regions are arranged discretely, The metal plate has a polygonal, circular, or elliptical shape, The second region is disposed between a plurality of the first regions. Electromagnetic wave attenuation film for use in the frequency range of 57 GHz to 90 GHz.

5. 3. The electromagnetic wave attenuation film according to claim 1, wherein the thin-film conductive layer and the planar inductor are spaced apart in the thickness direction of the dielectric substrate.

6. 6. The electromagnetic wave attenuation film according to claim 1, further comprising a topcoat layer on the thin film conductive layer.

7. 7. The electromagnetic wave attenuation film according to claim 6, wherein the top coat layer is impedance-matched to an air layer through which electromagnetic waves propagate.

8. 8. The electromagnetic wave attenuation film according to claim 7, wherein the top coat layer is mainly composed of an acrylic resin composition containing cyclohexyl (meth)acrylate as a monomer component.

9. 9. The electromagnetic wave attenuation film according to claim 8, wherein the top coat layer contains an ultraviolet absorbing agent and an ultraviolet scattering agent in an acrylic resin composition.

10. 10. The electromagnetic wave attenuation film according to claim 1, wherein the metal plate is made of any one of silver, copper, and aluminum.

11. 11. The electromagnetic wave attenuation film according to claim 1, wherein a plurality of the metal plates of the same shape and size are arranged at intervals of a predetermined range of values.

12. The electromagnetic wave attenuation film according to claim 1 , wherein the thin-film conductive layer is configured to be able to capture electromagnetic waves incident from the front side.

13. The electromagnetic wave attenuation film according to claim 1 , wherein the metal plate has a pair of opposing sides.

14. 14. The electromagnetic wave attenuation film according to claim 13, wherein the length of a pair of opposing sides of the metal plate is 0.25 mm or more and 4 mm or less.

15. 15. The electromagnetic wave attenuation film according to claim 1, wherein the thickness of the dielectric substrate is sufficiently thin relative to the attenuation center wavelength.

16. 16. The electromagnetic wave attenuation film according to claim 1, wherein the thickness of the dielectric substrate is less than 1 / 10 of the attenuation center wavelength.

17. An electromagnetic wave attenuation film described in any one of claims 1 to 16, wherein the metal plate is a polygon with rounded corners.

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